Shop by Manufacturer

Please Note

MarineEngine.com does not offer troubleshooting assistance or repair advice by email or by telephone. You are invited to join our public Boat Repair Forum to seek assistance from other members. You may also visit the Boat Motor Manuals section of our site to obtain a service manual.

Transmission problem on 12v71n

When I was returning from a long fishing trip, I noticed that the port engine revs kept dropping. Checked the port engine throttle/gear control & it had come right out of its bracket. The bracket was badly made and weak. Also now the port engine would not go into forward gear unless I revved up a lot & the transmission oil alarm came on. Checked oil in transmission & it was full, plus new, I had changed oil (40W) recently.
Got home slow & careful. Had new cable & bracket installed. Then at first the port engine would go into fwd after a 4 sec delay. Checked the oil pressure to Gear Box, it was 100 psi.
Checked the screen & found some clutch material, less than a teaspoon.
Cleaned it, new gasket etc.
Now there is NO transmission pressure. Port will not engage ANY gear. The Gear Box is an Allison.
I have a mechanic who is going to help me put in a new seal kit in the oil pump.
It's a HYDRECO Constant flow oil pump. IF the re-built pump still does not give transmission pressure, what else could it be & what should I do?

Re: Transmission problem on 12v71n

Time for a rebuild of the trans. If the trans is old and it has been a long time since the fluid has been changed, the new fluid will clean the lips seals of any debris and cause them to leak and the clutch packs will not engage fully and burn up the disks. Pull the whole unit and freshen it up.

Re: Transmission problem on 12v71n

Originally Posted by Docksidemarineservices

Time for a rebuild of the trans. If the trans is old and it has been a long time since the fluid has been changed, the new fluid will clean the lips seals of any debris and cause them to leak and the clutch packs will not engage fully and burn up the disks. Pull the whole unit and freshen it up.

Hi Dockside,
The engines and transmissions have less than 300 hrs since complete overhaul. The boat sat unused for 3 years before I bought it last year.
How can I test the Hydreco oil pump and the transmission to make sure which is causing the problem?
Re-building the transmission is a big cost and if possible I would like to avoid this.
Thanks.

Re: Transmission problem on 12v71n

Originally Posted by Docksidemarineservices

Get the actual model number off the unit and i will find the information for you. 300 hrs and 3 years of sitting can equal 10 to 20 years.

Hi, The model numbers on the pump are not visible. They were painted white on both engines, and when I scraped off the paint, there was no model number or plate. I did find another pump from a guy that had one off an old engine and the number was:
Model # 1413A-SP1
BTW, this old pump did not work either.
Do the pumps have specific rotation? In other words, does it matter if the pump is on a port or stbd engine?
thanks,
George

Re: Transmission problem on 12v71n

Re: Transmission problem on 12v71n

Okay, the latest:
Had the new kit put into the oil pump (Hydreco) and it was rebuilt using some of the parts from the spare I boought.
Installed it.
the oil pressure gauge showed NO pressure..... so we turned the adjustment nut clockwise. Suddenly oil comes out the oil filter......there is TOO MUCH pressure and my gauge is not working.
The guy I am working with has a gauge so we check the pressure. It is 130psi.
Try to put in FWD gear and it takes 5 secs..
REVERSE is immediate response.
The more we put the GB into gear & out the quicker the response. In other words she is improving?
Left it for the day.

Today I removed the gearbox oil. Replaced with NEW oil. Changed the oil filter. Made sure everything was tight etc.
Started up. My gearbox oil pressure gauge works....shows 150psi.
try going into FWD= 5 sec delay.
So now I have decided to give it a good run. I cannot take her out today because we have floods here in S.E Queensland with lots of crap in the water.
Maybe she will be okay. I can live with a 5 sec delay into gear rather than a gearbox off the engine & new clutch & seals etc.
What are your thoughts?

Re: Transmission problem on 12v71n

The lip seals are not going to fix themselves. There is a possibility of some debris that is stuck in the seal causing the delayed gear engagement. I would put some additive in the trans, IE...Lucas. If you start to notice longer delays, it will be time to pull the gear and replace the burned clutches and bad seals.

Re: Transmission problem on 12v71n

Originally Posted by Docksidemarineservices

The lip seals are not going to fix themselves. There is a possibility of some debris that is stuck in the seal causing the delayed gear engagement. I would put some additive in the trans, IE...Lucas. If you start to notice longer delays, it will be time to pull the gear and replace the burned clutches and bad seals.

This makes sense as the problem started AFTER I changed the Gear Box oil.
What is the name of the Lucas additive?
Thanks.
Kafue

Re: Transmission problem on 12v71n

Bad news!

Finally was able to take the boat for a run.
At idle the port gear box has just over 150 psi pressure. When I put it in gear, takes about 5 seconds to engage. BUT:
When I revved the engine up to get going, there is hardly any thrust. Tried a few times. Increased the pressure on the adjustment screw. No change. As soon as I put it in gear the pressure drops to 60 to 75 psi.
I think the gear box is going to need to be worked on. Whether it is the piston or seals I have no idea.
Damn! Besides the money, it is the best time for game fishing.
Damn!!!